Check valves of the type having a spring biased poppet mounted therein are oftentimes employed as relief valves in fluid circuits to relieve excess fluid pressures. The pressure setting of the poppet may be changed, for example, by either employing springs having different spring rates or by employing means associated with the spring to provide such variance. However, such a change normally requires a complete dismantling of the valve and does not always assure the precisely held pressure setting required in sophisticated fluid circuits.